Anybody feel more insecurity and jealously over their FWB dating others than their primary dating others?

I have compersion and more hearing about my husband’s dating. Conversely, hearing about my FWB’s dating makes me feel insecure and jealous. I suppose this is likely because my husband and I are on more stable ground, verses a relatively new (10 mos) and sometimes tumultuous, less stable situation?

FWB and I have become best friends, we use the L word, we have sleepovers, we share friends, and we spend 1-2 days a week together. We have awesome sexual chemistry and fun.

Things haven’t been bc perfect or easy though especially recently, as a matter of fact a number of you are going to stalk my post history and hate that I’m with FWB again/still, but I digress. I suppose the overarching uncertainty and doubt of our whole relationship are contributing factors to the jealously and insecurity yes?

FWB is a solo dating poly person. My fear is that he’ll end up leaving me for monogamy. But recently, he went on an “awesome date with great conversation, common interests, sense of humor, and chemistry” — and I couldn’t help but feel like “hey, I’m that person for you!!” — which I realize is bonkers. But better yet, he made a point to be like “she’s cool with poly, she knows about you, I told her you’re my bestie” etc. Which is sweet. I mean in an ideal world he slots in a cool primary that’s cool with his preexisting secondary and our relationship remains. And that’s what this could be, yet I’m still jealous.

He’s been bad with time management before, and bad with making me feel appreciated, though he’s getting better with both. Though I guess if I’ve felt the scarcity of these things in previous when he was solo, it only makes sense I’d be concerned those issues will be exacerbated when I have to share him with someone new he’ll be enamored with, right?

Help?